Natural products have a proven record of providing a significant fraction, either directly or as lead compounds, of human medicines. Among natural products, the terpenoids (isoprenoids) stand out as being the largest class (>50,000 already known), with the 20-carbon diterpenoids targeted here forming a significant fraction of these (>12,000 known). The extensive diversification of diterpenoids indicates that the manifold hydrocarbon skeletons that can be formed from this C20 backbone, particularly the decalin core ring structure found in the labdane-related diterpenoids (>7,000 known), provide privileged scaffolds for derivation of biological activity. Indeed, a number of these labdane-related diterpenoids are used as pharmaceuticals (e.g., the antibiotic mutilins) or are being investigated for such use (e.g., the tanshinones, triptolide, andrographolide, etc.). In addition, we have contributed to the discovery that the human pathogen Mycobacterium tuberculosis utilizes labdane-related diterpenoid metabolism in construction of an immune-modulatory factor. Accordingly, we propose here to continue our productive studies of the biosynthetic enzymes required to produce bioactive diterpenoids. Specifically, we will build on our previous work in this area, which includes investigations of enzymatic structure-function that have provided novel biosynthetic access to an array of diterpenoids, as well as elucidation of strategically selected diterpenoid metabolic networks. This MIRA proposal covers our systematic studies in this area, advancing our long-term goal of engineering enzymes and metabolic pathways for the production of targeted libraries and specific individual terpenoid ?natural? products, which are being already using for investigation of pharmaceutical utility.